40 Background: To restore innate tumor surveillance that is lost in cancer patients, a tumoricidal agent may have synergistic activity with an immune checkpoint inhibitor. Herein, we report on a retrospective analysis of our clinical experience using trabectedin, an alkylating agent, and nivolumab, a PD-1 inhibitor in advanced soft tissue sarcoma. Methods: Twenty previously treated STS patients received trabectedin (1.5 mg/m2 continuous intravenous infusion, CIV, for 24 hours) every 3 weeks, and nivolumab (3 mg/kg IV over 30 minutes) every 2 weeks. Safety/toxicity was analyzed using the NIH/NCI CTCAE v.4.03. Tumor responses were assessed by RECIST v1.1 and immune-related response criteria (irRECIST). Results: Histologic subtypes in 20 patients include undifferentiated pleomorphic sarcoma (UPS; n = 7), leiomyosarcoma (n = 5), synovial sarcoma (n = 2), myxoid liposarcoma (n = 4) and chondrosarcoma (n = 2). All patients had metastatic disease and a median of 4 lines of prior chemotherapy. Safety analysis (n = 20): Grade 3 treatment emergent adverse events include anemia (n = 2), fatigue (n = 1), decreased platelet count (n = 1), decreased granulocyte count (n = 1) and increased creatine kinase (n = 1). Efficacy analysis (n = 17): Seventeen patients were followed for at least 6 months and their results are reported here. There were 4 partial responses (UPS = 1, myxoid liposarcoma = 1, chondrosarcoma = 1, leiomyosarcoma = 1), 7 stable disease, and 6 progressive disease, with best overall response rate of 23.5%, median progression free survival (PFS) of > 11.6 months (range: 2.3- > 16.9 months), median overall survival (OS) of > 14.2 months (4.5- > 24.0 months), 6 month PFS rate of 64.7%, and 6 month OS rate of 94.1%. In a Phase 3 study, the median PFS was 4.2 months using trabectedin alone (Demetri et al., 2015). Conclusions: Taken together, the data suggest that paired administration of trabectedin and nivolumab is safe, and that this chemo-/immuno-therapy approach has synergistic activity.
